System and method for monitoring ablation size

ABSTRACT

A system for monitoring ablation size includes a power source including a microprocessor for executing one or more control algorithms. A microwave antenna is configured to deliver microwave energy from the power source to tissue to form an ablation zone. A plurality of spaced-apart electrodes is operably disposed along a length of the microwave antenna. The plurality of spaced-apart electrodes is disposed in electrical communication with one another and each of the plurality of spaced-apart electrodes has a threshold impedance associated therewith corresponding to the radius of the ablation zone.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation application of U.S. patent application Ser. No. 14/306,865, filed on Jun. 17, 2014, now U.S. Pat. No. 9,820,813, which is a divisional application of U.S. patent application Ser. No. 12/692,856, filed on Jan. 25, 2010, now U.S. Pat. No. 8,764,744, the entire contents of all of the foregoing applications are incorporated by reference herein.

BACKGROUND

Technical Field

The present disclosure relates to systems and methods that may be used in tissue ablation procedures. More particularly, the present disclosure relates to systems and methods for monitoring ablation size during tissue ablation procedures in real-time.

Background of Related Art

In the treatment of diseases such as cancer, certain types of cancer cells have been found to denature at elevated temperatures (which are slightly lower than temperatures normally injurious to healthy cells). These types of treatments, known generally as hyperthermia therapy, typically utilize electromagnetic radiation to heat diseased cells to temperatures above 41° C. while maintaining adjacent healthy cells at lower temperatures where irreversible cell destruction will not occur. Procedures utilizing electromagnetic radiation to heat tissue may include ablation of the tissue.

Microwave ablation procedures, e.g., such as those performed for menorrhagia, are typically done to ablate the targeted tissue to denature or kill the tissue. Many procedures and types of devices utilizing electromagnetic radiation therapy are known in the art. Such microwave therapy is typically used in the treatment of tissue and organs such as the prostate, heart, and liver.

One non-invasive procedure generally involves the treatment of tissue (e.g., a tumor) underlying the skin via the use of microwave energy. The microwave energy is able to non-invasively penetrate the skin to reach the underlying tissue. However, this non-invasive procedure may result in the unwanted heating of healthy tissue. Thus, the non-invasive use of microwave energy requires a great deal of control.

Currently, there are several types of systems and methods for monitoring ablation zone size. In certain instances, one or more types of sensors (or other suitable devices) are operably associated with the microwave ablation device. For example, in a microwave ablation device that includes a monopole antenna configuration, an elongated microwave conductor may be in operative communication with a sensor exposed at an end of the microwave conductor. This type of sensor is sometimes surrounded by a dielectric sleeve.

Typically, the foregoing types of sensors are configured to function (e.g., provide feedback to a controller for controlling the power output of a power source) when the microwave ablation device is inactive, i.e., not radiating. That is, the foregoing sensors do not function in real-time. Typically, the power source is powered off or pulsed off when the sensors are providing feedback (e.g., tissue temperature) to the controller and/or other device(s) configured to control the power source.

SUMMARY

The present disclosure provides a system for monitoring ablation size in real-time. The system includes a power source. A microwave antenna is configured to deliver microwave energy from the power source to tissue to form an ablation zone. A plurality of spaced-apart electrodes is operably disposed along a length of the microwave antenna. The electrodes are disposed in electrical communication with one another. Each of the electrodes has a threshold impedance associated therewith corresponding to the radius of the ablation zone.

The present disclosure provides a microwave antenna adapted to connect to a power source configured for performing an ablation procedure. The microwave antenna includes a radiating section configured to deliver microwave energy from the power source to tissue to form an ablation zone. The microwave antenna includes a plurality of spaced-apart electrodes operably disposed along a length of the microwave antenna. The electrodes are disposed in electrical communication with one another. Each of the electrodes has a threshold impedance associated therewith corresponding to the radius of the ablation zone.

The present disclosure also provides a method for monitoring tissue undergoing ablation. The method includes the initial step of transmitting microwave energy from a power source to a microwave antenna to form a tissue ablation zone. A step of the method includes monitoring one or more electrodes impedance along the microwave antenna as the tissue ablation zone forms. Triggering a detection signal when a predetermined electrode impedance is reached at the at least one electrode along the microwave antenna is another step of the method. The method includes adjusting the amount of microwave energy from the power source to the microwave antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a system for monitoring ablation size according to an embodiment of the present disclosure;

FIG. 2 is partial, side view illustrating internal components of a distal tip of a microwave antenna depicted in FIG. 1;

FIG. 3 is a functional block diagram showing a power source for use with the system depicted in FIG. 1;

FIG. 4A is a schematic, plan view of a tip of the microwave antenna depicted in FIG. 2 illustrating radial ablation zones having a generally spherical configuration;

FIG. 4B is a schematic, plan view of a tip of the microwave antenna depicted in FIG. 2 illustrating radial ablation zones having a generally ellipsoidal configuration;

FIG. 5A is a schematic, plan view of a portion of the microwave antenna depicted in FIG. 1 showing a sequenced insertion of the microwave antenna into tissue;

FIG. 5B is a graphical representation of corresponding impedances associated with respective electrodes of the microwave antenna depicted in FIG. 5A;

FIG. 6 is a flow chart illustrating a method for monitoring temperature of tissue undergoing ablation in accordance with the present disclosure;

FIG. 7 is partial, side view illustrating internal components of a distal tip of a microwave antenna according to an alternate embodiment of the present disclosure; and

FIG. 8 is a functional block diagram showing a power source for use with the microwave antenna depicted in FIG. 7.

DETAILED DESCRIPTION

Embodiments of the presently disclosed system and method are described in detail with reference to the drawing figures wherein like reference numerals identify similar or identical elements. As used herein and as is traditional, the term “distal” refers to the portion which is furthest from the user and the term “proximal” refers to the portion that is closest to the user. In addition, terms such as “above”, “below”, “forward”, “rearward”, etc. refer to the orientation of the figures or the direction of components and are simply used for convenience of description.

Referring now to FIGS. 1 and 2, and initially with reference to FIG. 1, a system for monitoring ablation size in accordance with an embodiment of the present disclosure is designated 10. A microwave antenna 12 operably couples to generator 100 and includes a controller 200 that connects to the generator 100 via a flexible coaxial cable 14. In this instance, generator 100 is configured to provide microwave energy at an operational frequency from about 500 MHz to about 10 GHz. Microwave antenna 12 includes a radiating section or portion 16 (FIGS. 1 and 2) that is connected by a feedline or shaft 18 to coaxial cable 14 and extends from the proximal end of the microwave antenna 12. Cable 14 includes an inner conductor 13 that is operably disposed within the shaft 18 and in electrical communication with a radiating section 16 (FIGS. 1 and 2). Microwave antenna 12 couples to the cable 14 through a connection hub 22. The connection hub 22 includes an outlet fluid port 24 and an inlet fluid port 26 connected in fluid communication with a sheath or cannula 28 (FIG. 2). Cannula 28 is configured to circulate coolant fluid 30 from ports 24 and 26 around the antenna assembly 12 via respective fluid lumens 32 and 34 (FIG. 2). Ports 24 and 26, in turn, couple to a supply pump 40. For a more detailed description of the microwave antenna 12 and operative components associated therewith, reference is made to commonly-owned U.S. Pat. No. 8,118,808, filed on Mar. 10, 2009, the entire contents of which are incorporated by reference herein.

With continued reference to FIGS. 1 and 2, two or more spaced-apart electrodes 52 and 54 are operably disposed along a length of the shaft 18. More particularly, the electrodes 52 and 54 are disposed in proximity to a distal end 19 of the shaft 18. In the embodiment illustrated in FIG. 2, electrodes 52 include a series of proximal spaced-apart electrodes 52 a-52 h and a distal electrode 54. As defined herein, a series of electrodes is meant to mean two or more electrodes. For purposes herein, the series of proximal spaced-apart electrodes 52 a-52 h referred to proximal electrodes 52. The configuration of the electrodes 52 and 54 enables physical space sampling of an ablation site. More particularly, in one particular embodiment, during the delivery of microwave energy to the microwave antenna 12, impedance between one or more of the proximal electrodes 52, e.g., proximal electrode 52 a, and the distal electrode 54 is measured and compared with known impedance values associated with the microwave antenna 12 and/or proximal electrodes 52, e.g., proximal electrode 52 a. The configuration of each proximal electrodes 52 a-52 h and distal electrode 54 provides a separate closed loop path for current to flow, i.e., an electrical circuit, when the microwave antenna 12 is inserted into tissue at a target tissue site. Impedance is measured between each proximal electrode 52 a-52 h and the distal electrode 54, as described in greater detail below.

Proximal electrodes 52 a-52 h may be formed from any suitable conductive or partially conductive material. For example, proximal electrodes 52 a-52 h may be formed from copper, silver, gold, etc. Proximal electrodes 52 a-52 h are operably positioned along an outer peripheral surface 38 of the shaft 18 in a manner suitable for the intended purposes described herein. In embodiments, the proximal electrodes 52 a-52 h may extend circumferentially along the outer peripheral surface 38 or partially along a length of the shaft 18. In the illustrative embodiment, proximal electrodes 52 a-52 h extend partially along the outer peripheral surface 38 in a linear manner forming a generally linear array along the outer peripheral surface 38 of the shaft 18. Proximal electrodes 52 a-52 h may be secured to the outer peripheral surface 38 and/or the shaft 18 via any suitable method(s). In one particular embodiment, the proximal electrodes 52 a-52 h are secured to the outer peripheral surface 38 via an epoxy adhesive (or other suitable adhesive). Proximal electrodes 52 a-52 h are in operative communication with one or more modules, e.g., ablation zone control module 232 (AZCM), associated with the generator 100 and/or controller 200. To this end, a portion of the proximal electrodes 52 a-52 h connects to one or more electrical leads (not explicitly shown) that provide an electrical interface for the proximal electrodes 52 a-52 h and the AZCM 232. Moreover, the electrical leads provide an electrical interface that supplies current, i.e., from a current source (or other suitable device configured to generate current, voltage source, power source, etc.) to the proximal electrodes 52 a-52 h.

In certain embodiments, one or more sensors, e.g., sensors 53 a-53 h, may be in operative communication with a respective one or corresponding proximal electrode 52 a-52 h (as best seen in FIG. 2). In this instance, the sensors 53 a-53 h may be configured to provide real-time information pertaining to the proximal electrodes 52 a-52 h. More particularly, the sensors 53 a-53 h may be configured to provide real-time information pertaining to one or more electrical parameters (e.g., impedance, power, voltage, current, etc.) and/or other parameters associated with the proximal electrodes 52 a-52 h. More particularly, the sensors 53 a-53 h may be in the form of one or more types of thermal sensors such as, for example, a thermocouple, a thermistor, an optical fiber, etc. In one particular embodiment, the sensors 53 a-53 h are thermocouples 53 a-53 h.

Distal electrode 54 may be formed from any suitable conductive or partially conductive material, e.g., copper, silver, gold, etc. Distal electrode 54 may have any suitable configuration. For illustrative purposes, distal electrode 54 is shown operably disposed at a distal tip 21 of the shaft 18. In the illustrated embodiment, distal electrode 54 defines a conductive tissue piercing tip. In this instance, the distal electrode 54 facilitates insertion of the microwave antenna 12 into tissue at a target tissue site. Alternatively, distal electrode 54 may have a relatively blunt configuration. An electrical lead (not explicitly shown) provides an electrical interface for returning current from the distal electrode 54 back to the current source. In certain embodiments, distal electrode 54 may be in operative communication with one or more modules, e.g., AZCM 232, associated with the generator 100 and/or controller 200. In this instance, the electrical lead may provide an electrical interface for the distal electrode 54 and the AZCM 232.

In certain embodiments, one or more sensors, e.g., sensor 55, may be in operative communication with the distal electrodes 54 (see FIG. 2, for example) and may provide information relevant to the proper operation of distal electrode 54 to the AZCM 232. Sensor 55 may be any suitable type of sensor such as, for example, one or more types of thermal sensors previously described above, e.g., a thermocouple.

A dielectric sheath 60 having a suitable thickness and made from a suitable material is operably positioned along a length of the microwave antenna 12 and substantially encases the proximal electrodes 52 a-52 h and distal electrode 54 in a manner that allows current to flow from the proximal electrodes 52 a-52 h to the distal electrode 54. Dielectric sheath 60 may be made from any suitable material and may be affixed to the microwave antenna 12 by any suitable affixing methods. In the illustrated embodiment, the dielectric sheath 60 is a vapor deposited dielectric material, such as, for example, parylene, that is applied to the microwave antenna 12. Substantially encasing the microwave antenna 12 with dielectric sheath 60 results in capacitive impedance that can allow RF current flow to/from the electrodes 52 a-52 h and tissue. More particularly, during transmission of microwave energy from the generator 100 to the microwave antenna 12 and when the proximal electrodes 52 a-52 h and distal electrode 54 are positioned within tissue adjacent a target tissue site, current flows from proximal electrodes 52 a-52 h to the electrode 54. Dielectric sheath 60 is configured to focus current densities “I” at the proximal electrodes 52 a-52 h and/or the distal electrode 54, which, in turn, provides comprehensive and/or more accurate measurements of impedance at the proximal electrode 52 a-52 h, as best seen in FIG. 2. In certain embodiments, the dielectric sheath 60 may fully encase the proximal electrodes 52 a-52 h and distal electrode 54. In this instance, the dielectric sheath 60 includes a thickness that allows current to pass from the proximal electrodes 52 a-52 h through the dielectric sheath 60 and to the distal electrode 54. In one particular embodiment, the thickness of the dielectric material of the dielectric sheath 60 ranges from about 0.0001 inches to about 0.001 inches.

As mentioned above, proximal electrodes 52 a-52 h (and in some instances distal electrode 54) is in operative communication with the generator 100 including AZCM 232 and/or controller 200. More particularly, the proximal electrodes 52 a-52 h and distal electrode 54 couple to the generator 100 and/or controller 200 via one or more suitable conductive mediums (e.g., a wire or cable 56) that extends from proximal electrodes 52 a-52 h and distal electrode 54 to the proximal end of the microwave antenna 12 and connects to the generator 100 (see FIG. 2, for example). In the illustrated embodiment, wire 56 is operably disposed within cable 14. Wire 56 electrically connects to the proximal electrodes 52 a-52 h and distal electrode 54 via the one or more leads previously described. The configuration of wire 56, proximal electrodes 52 a-52 h and distal electrode 54 forms a closed loop current path when the electrodes 52 and distal electrode 54 are positioned within tissue adjacent a target tissue site. In the illustrated embodiment, the wire 56 extends along the outer peripheral surface 38 of the shaft 18 and is encased by the dielectric sheath 60. Alternatively, the wire 56 may extend within and along a length of the shaft 18.

With reference to FIG. 3, a schematic block diagram of the generator 100 is illustrated. The generator 100 includes a controller 200 including one or more modules (e.g., an AZCM 232), a power supply 137, a microwave output stage 138. In this instance, generator 100 is described with respect to the delivery of microwave energy. The power supply 137 provides DC power to the microwave output stage 138 which then converts the DC power into microwave energy and delivers the microwave energy to the radiating section 16 of the microwave antenna 12 (see FIG. 2). In the illustrated embodiment, a portion of the DC power is directed to the AZCM 232, described in greater detail below. The controller 200 may include analog and/or logic circuitry for processing sensed analog responses, e.g., impedance response, generated by the proximal electrodes 52 a-52 h and determining the control signals that are sent to the generator 100 and/or supply pump 40 via the microprocessor 235. More particularly, the controller 200 accepts one or more signals indicative of impedance associated with proximal electrodes 52 a-52 h adjacent an ablation zone and/or the microwave antenna 12, namely, the signals generated by the AZCM 232 as a result of the impedance measured and/or produced by proximal electrodes 52 a-52 h. One or more modules e.g., AZCM 232, of the controller 200 monitors and/or analyzes the impedance produced by the proximal electrodes 52 a-52 h and determines if a threshold impedance has been met. If the threshold impedance has been met, then the AZCM 232, microprocessor 235 and/or the controller 200 instructs the generator 100 to adjust the microwave output stage 138 and/or the power supply 137 accordingly. Additionally, the controller 200 may also signal the supply pump to adjust the amount of cooling fluid to the microwave antenna 12 and/or the surrounding tissue.

The controller 200 includes microprocessor 235 having memory 236 which may be volatile type memory (e.g., RAM) and/or non-volatile type memory (e.g., flash media, disk media, etc.). In the illustrated embodiment, the microprocessor 235 is in operative communication with the power supply 137 and/or microwave output stage 138 allowing the microprocessor 235 to control the output of the generator 100 according to either open and/or closed control loop schemes. The microprocessor 235 is capable of executing software instructions for processing data received by the AZCM 232, and for outputting control signals to the generator 100 and/or supply pump 40, accordingly. The software instructions, which are executable by the controller 200, are stored in the memory 236.

In accordance with the present disclosure, the microwave antenna 12 is configured to create an ablation zone “A” having any suitable configuration, such as, for example, spherical (FIG. 4A), hemispherical, ellipsoidal (FIG. 4B where the ablation zone is designated “A-2”), and so forth. In one particular embodiment, microwave antenna 12 is configured to create an ablation zone “A” that is spherical (FIG. 4A). To facilitate understanding of the present disclosure, ablation zone “A” is being defined having a plurality of concentric ablation zones having radii r₁-r₈ when measured from the center of the ablation zone “A,” collectively referred to as radii r.

With reference to FIGS. 5A and 5B, proximal electrodes 52 a-52 h in combination with distal electrode 54 are configured to provide comprehensive monitoring of an ablation zone “A” (FIGS. 4A and 5A at microwave position J). More particularly, the concept of the integration of impedance Z associated with proximal electrodes 52 over time may be used to indicate tissue damage, e.g., death or necrosis. For a given microwave antenna 12, each of the proximal electrodes 52 a-52 h has a predetermined threshold impedance Z associated therewith. The predetermined threshold impedance Z associated with a corresponding electrode 52 a-52 h, e.g., electrode 52 a, and a corresponding radius “r,” e.g., r1, may be determined via any suitable methods. For example, predetermined threshold impedances Z may be determined via known experimental test data, model equations, functions and graphs, or combination thereof.

In one particular embodiment, a control algorithm of the present disclosure uses known (or in certain instances predicted) threshold impedances Z at specific radii to create an ablation zone “A” having a radius “r.” That is, impedances Z associated with proximal electrodes 52 a-52 h that correspond to specific radii are compiled into one or more look-up tables “D” and are stored in memory, e.g., memory 236, accessible by the microprocessor 235 and/or the AZCM 232 (FIG. 3). The AZCM 232 includes control circuitry that receives information from the proximal electrodes 52 a-52 h, and provides the information and the source of the information (e.g., the particular proximal electrode 52 providing the information) to the controller 200 and/or microprocessor 235. More particularly, AZCM 232 monitors the impedance Z at the proximal electrodes 52, e.g., proximal electrode 52 a, and triggers a command signal in response to the proximal electrode 52 a reaching a predetermined impedance Z such that the electrosurgical output power from the generator 100 may be adjusted (see FIG. 5A at microwave antenna 12 position F).

AZCM 232 may be configured to monitor impedance Z at the proximal electrodes 52 a-52 h by any known method(s). For example, in one particular embodiment, the AZCM 232 utilizes one or more equations (V=I×Z) to calculate the impedance at a particular electrode 52 a-52 h. In this instance, the voltage V and current I is known and the AZCM 232 calculates the impedance Z. Alternatively, or in combination therewith, the sensor(s) 53 a-53 h may provide thermal measurements at a respective electrode 52 a-52 h. With the impedance of a respective proximal electrode 52 a-52 h calculated and/or determined, AZCM 232, microprocessor 235 and/or controller 200 may access the one or more look-up tables “D” and confirm that the threshold impedance Z has been met and, subsequently, instruct the generator 100 to adjust the amount of microwave energy being delivered to the microwave antenna 12, see FIG. 5B at corresponding graphical representation F. This combination of events will provide an ablation zone “A” with a radius approximately equal to r3, i.e., an ablation zone approximately equal to 3 cm by 1 cm. It should be noted, that in this instance, the ablation zone “A” is more ellipsoidal than spherical. In embodiments, one or more control algorithms may utilize interpolation between the radii associated with the electrodes 52 a-52 h to calculate impedance between discreetly measured radii, e.g., impedance measured between electrode 52 a and electrode 52 b. More particularly, various (and commonly known) interpolation techniques may be utilized via curve fitting along the electrodes 52 a-52 h.

In certain instances, the one or more data look-up tables may be stored into memory during the manufacture process of the generator 100 and/or controller 200 or downloaded during programming; this is particularly useful in the instance where the generator 100 is configured for use with a single type of microwave antenna. Alternatively, the one or more data look-up tables may be downloaded into memory 236 at a time prior to use of the system 10; this is particularly useful in the instance where the generator 100 is configured for use with multiple microwave antennas that are configured to perform various ablation procedures.

In one particular embodiment, data look-up table “D” may be stored in a memory storage device 73 associated with the microwave antenna 12. More particularly, a data look-up table “D” may be stored in a memory storage device 73 operatively associated with the microwave antenna 12 and may be downloaded, read and stored into microprocessor 235 and/or memory 236 and, subsequently, accessed and utilized in a manner described above; this would dispose of the step of reprogramming the generator 100 and/or controller 200 for a specific microwave antenna. More particularly, the memory storage device 73 may be operably disposed on the microwave antenna 12, such as, for example, on or adjacent the hub 22 (FIG. 1). In this instance, when a user connects the microwave antenna 12 to the generator 100, the information contained in the memory storage device may be automatically read, downloaded and stored into the generator 100 and accessed for future use. The memory storage device 73 may also include information pertaining to the microwave antenna 12. Information, such as, for example, the type of microwave antenna, the type of tissue that the microwave antenna is configured to treat, the type of ablation zone desired, etc., may be stored into the storage device 73 associated with the microwave antenna 12.

In the embodiment illustrated in FIG. 1, the generator 100 is shown operably coupled to fluid supply pump 40. The supply pump 40 is, in turn, operably coupled to a supply tank 44. In embodiments, the microprocessor 235 is in operative communication with the supply pump 40 via one or more suitable types of interfaces, e.g., a port 140 operatively disposed on the generator 100, that allows the microprocessor 235 to control the output of a cooling fluid 30 from the supply pump 40 to the microwave antenna 12 according to either open and/or closed control loop schemes. The controller 200 may signal the supply pump 40 to control the output of cooling fluid 30 from the supply tank 44 to the microwave antenna 12. In this way, cooling fluid 30 is automatically circulated to the microwave antenna 12 and back to the supply pump 40. In certain embodiments, a clinician may manually control the supply pump 40 to cause cooling fluid 30 to be expelled from the microwave antenna 12 into and/or proximate the surrounding tissue.

Operation of system 10 is now described. For illustrative purposes, proximal electrodes 52 a-52 h may be considered as individual anodes and distal electrode 54 may be considered as a cathode. Each of the proximal electrodes 52 a-52 h includes a predetermined threshold impedance Z that has been previously determined by any of the aforementioned methods, e.g., experimental test data. Initially, microwave antenna 12 is connected to generator 100. In one particular embodiment, one or more modules, e.g., AZCM 232, associated with the generator 100 and/or controller 200 reads and/or downloads data, e.g., the type of microwave antenna, the type of tissue that is to be treated, data look-up tables, etc., from storage device 73 associated with the antenna 12. In the present example, the AZCM module 232 recognizes the microwave antenna 12 as having 8 proximal electrodes 52 a-52 h each with a predetermined threshold impedance Z that corresponds to a specific ablation zone “A.” In one particular embodiment, the generator 100 prompts a user to enter the desired ablation zone size, e.g., ablation zone equal to 5 cm by 5 cm having a generally spherical configuration, see FIGS. 4A and 5A at microwave antenna 12 position J. After a user inputs the desired ablation zone size information, the AZCM 232 matches the desired ablation zone size with the particular electrode 52 a-52 h, e.g., proximal electrode 52 h. The AZCM 232 sets the threshold impedance Z, e.g., Z ablated, for that particular proximal electrode. Thereafter, the generator 100 may be activated supplying microwave energy to the radiating section 16 of the microwave antenna 12 such that the tissue may be ablated.

AZCM 232 transmits DC current (or in some instances an RF signal, e.g., in the KHz or low MHz frequency spectrum) to each of the proximal electrodes 52 a-52 h. Prior to insertion of microwave antenna 12 into tissue “T”, impedance Z associated with each of the plurality of proximal electrodes 52 a-52 h is relatively high, e.g., infinite; this is because an open circuit exists between the proximal electrodes 52 a-52 h and the distal electrode 54. Microwave antenna 12 including proximal electrodes 52 a-52 h may then be positioned within tissue (see FIGS. 5A and 5B at microwave antenna 12 position E and corresponding graph at position E, respectively) adjacent a target tissue site. Impedance Z associated with each of the plurality of proximal electrodes 52 a-52 h is relatively low, e.g., non-zero; this is because uncooked tissue has a finite or infinitesimal impedance. During tissue ablation, the AZCM 232 monitors impedance Z of the proximal electrodes 52 a-52 h. During tissue ablation, when a predetermined threshold impedance is reached (such as the impedance Z that corresponds to radius r8) at the particular proximal electrode 52 a-52 h, e.g., electrode 52 h, and is detected by the AZCM 232, the AZCM 232 instructs the generator 100 to adjust the microwave energy accordingly. In the foregoing sequence of events, the proximal electrodes 52 a-52 h, distal electrode 54 and AZCM 232 function in real-time controlling the amount of microwave energy to the ablation zone such that a uniform ablation zone of suitable proportion is formed with minimal or no damage to adjacent tissue.

It should be noted that at any time during the ablation procedure, a user may adjust the previously inputted ablation zone size information. More particularly, if a user determines that during the course of the microwave ablation procedure the original ablation zone size needs to be adjusted, e.g., original ablation zone size is too big or too small, a user may simply input the new ablation zone size, and the AZCM 232 will adjust automatically. For example, if during the above example a user decides to adjust the ablation zone size to 4 cm by 4 cm (see FIGS. 5A and 5B at microwave antenna position I) the AZCM 232 monitors proximal electrode 52 e until proximal electrode 52 e reaches the predetermined threshold impedance Z.

With reference to FIG. 5 a method 400 for monitoring tissue undergoing ablation is illustrated. At step 402, microwave energy from a generator 100 is transmitted to a microwave antenna 12 adjacent a tissue ablation site. At step, 404, one or more electrodes' impedance at the ablation site is monitored. At step 406, a detection signal is triggered when a predetermined electrode impedance is reached at the one or more electrodes along the microwave antenna. At step 408, the amount of microwave energy from the generator 200 to the microwave antenna may be adjusted.

From the foregoing and with reference to the various figure drawings, those skilled in the art will appreciate that certain modifications can also be made to the present disclosure without departing from the scope of the same. For example, the system 10 may be adapted to connect to an RF electrosurgical power source, e.g., an RF generator that includes or is in operative communication with one or more controllers 200 including an AZCM 232.

While the electrodes 52 have been described herein as including a series of proximal electrodes 52 a-52 h and a distal electrode 54 that is positioned at a distal tip 21 of the shaft 18, it is within the purview of the present disclosure that the distal electrode 54 may be positioned anywhere along the shaft 18, e.g., positioned adjacent the series of proximal electrodes 52 a-52 h. Or, in another embodiment, a distal electrode 54 may not be utilized. In this instance, one of the series of proximal electrodes 52 a-52 h may be configured to function in a manner as described above with respect to distal electrode 54.

In certain embodiments, it may prove useful not to utilize a lead wire 56 that couples to distal electrode 54. In this instance, inner conductor 13 takes the place of the lead wire 56 and operably couples to the distal electrode 54, see FIG. 7, for example. More particularly, one or more types of DC blocks 58 are operatively associated with the microwave antenna 12. More particularly, DC block 58 is operably disposed within the generator 100 and in electrical communication with the inner conductor 13, shown schematically in FIG. 8. The DC block 58 prevents and/or limits direct current (DC) frequencies present at the distal electrode 54 from interfering with the microwave signals produced by the radiating section 16. DC block 58 may be configured in a manner that is conventional in the art. More particularly, DC block 58 may include one or more capacitors “C” configured in series with inner conductor 13 of the coaxial conductor 14, in series with an outer conductor (not explicitly shown) of the coaxial conductor 14, or in series with both the inner conductor 13 and outer conductor of the coaxial conductor 14. DC block 58 may be configured to function as a notch filter and designed to allow impedance measurement signals, i.e., impedance measurement signals that are in the KHz frequency range. In the embodiment illustrated in FIG. 7, lead wire 56 couples to the plurality of electrodes 52 a-52 h in a manner described above. Lead wire 56 is dimensioned to accommodate a respective RF signal that is transmitted to the distal electrode 54 and/or plurality of electrodes 52 a-52 h from the AZCM 232.

AZCM 232 is configured to transmit an RF impedance measurement signal to the proximal electrodes 52 a-52 h and/or the distal electrode 54. In the embodiment illustrated in FIG. 8, AZCM is configured to transmit an RF impedance measurement signal to the proximal electrodes 52 a-52 h and/or the distal electrode 54 that ranges from about 3 KHz to about 300 MHz.

Operation of system 10 that includes a generator 100 with a DC block 58 that is in operative communication with a microwave antenna 12 is substantially similar to that of a generator 100 without a DC block 58 and, as a result thereof, is not described herein.

While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto. 

What is claimed is:
 1. A system for monitoring ablation size, comprising: a power source; and a microwave antenna configured to transmit microwave energy from the power source to tissue to form an ablation zone, the microwave antenna including: an elongate shaft; a plurality of proximal spaced-apart electrodes disposed on the elongate shaft, each of the plurality of proximal spaced-apart electrodes having a threshold impedance associated therewith corresponding to a radius of the ablation zone; a distal electrode disposed on the elongate shaft distally of the plurality of proximal spaced-apart electrodes; a feedline having a distal radiating section disposed within the elongate shaft, the distal radiating section detached and electrically distinct from the distal electrode; a first sensor disposed on at least one of the plurality of proximal spaced-apart electrodes; and a second sensor disposed on the distal electrode, wherein a closed loop path is present between each electrode of the plurality of proximal spaced-apart electrodes and the distal electrode such that impedance is measurable between each electrode of the plurality of proximal spaced-apart electrodes and the distal electrode, and wherein the microwave antenna includes a wire serially connecting each of the plurality of proximal spaced-apart electrodes.
 2. The system according to claim 1, wherein the plurality of proximal spaced-apart electrodes is disposed along a longitudinal axis of the elongate shaft and in electrical communication with one another.
 3. The system according to claim 1, wherein the elongate shaft includes a distal tip and the distal electrode is disposed at the distal tip.
 4. The system according to claim 1, wherein the microwave antenna includes a dielectric sheath positioned along the elongate shaft and encasing the plurality of proximal spaced-apart electrodes and the distal electrode to allow current to flow from the plurality of proximal spaced-apart electrodes to the distal electrode.
 5. The system according to claim 1, wherein the plurality of proximal spaced-apart electrodes is disposed in a linear configuration on a distal portion of the elongate shaft.
 6. The system according to claim 1, further comprising an ablation zone control module in operative communication with the microwave antenna and the power source and configured to instruct the power source to adjust a parameter of the microwave energy based on a signal corresponding to the impedance measured between the first and second sensors.
 7. The system according to claim 1, further comprising a fluid pump configured to supply a cooling fluid to the microwave antenna for cooling the microwave antenna.
 8. A microwave antenna for delivering microwave energy to tissue to form an ablation zone, the microwave antenna comprising: an elongate shaft; a plurality of proximal spaced-apart electrodes disposed on the elongate shaft, each of the plurality of proximal spaced-apart electrodes having a threshold impedance associated therewith corresponding to a radius of the ablation zone; a distal electrode disposed on the elongate shaft distally of the plurality of proximal spaced-apart electrodes; a feedline having a distal radiating section disposed within the elongate shaft, the distal radiating section detached and electrically distinct from the distal electrode; a first sensor disposed on at least one of the plurality of proximal spaced-apart electrodes; and a second sensor disposed on the distal electrode, the first and second sensors being longitudinally spaced from one another along a longitudinal axis of the elongate shaft, wherein a closed loop path is present between each electrode of the plurality of proximal spaced-apart electrodes and the distal electrode such that impedance is measurable between each electrode of the plurality of proximal spaced-apart electrodes and the distal electrode, and further comprising a wire serially connecting each of the plurality of proximal spaced-apart electrodes.
 9. The microwave antenna according to claim 8, wherein the plurality of proximal spaced-apart electrodes is disposed along the longitudinal axis of the elongate shaft and in electrical communication with one another.
 10. The microwave antenna according to claim 8, wherein the elongate shaft includes a distal tip and the distal electrode is disposed at the distal tip.
 11. The microwave antenna according to claim 8, further comprising a dielectric sheath positioned along the elongate shaft and encasing the plurality of proximal spaced-apart electrodes and the distal electrode to allow current to flow from the plurality of proximal spaced-apart electrodes to the distal electrode.
 12. The microwave antenna according to claim 8, wherein the plurality of proximal spaced-apart electrodes is disposed in a linear configuration on a distal portion of the elongate shaft.
 13. A microwave antenna for delivering microwave energy to tissue to form an ablation zone, the microwave antenna comprising: an elongate shaft; a plurality of proximal spaced-apart electrodes disposed on the elongate shaft; a distal electrode disposed on the elongate shaft distally of the plurality of proximal spaced-apart electrodes; and a feedline having a distal radiating section disposed within the elongate shaft, the distal radiating section detached and electrically distinct from the distal electrode; wherein a closed loop path is present between each electrode of the plurality of proximal spaced-apart electrodes and the distal electrode such that impedance is measurable between each electrode of the plurality of proximal spaced-apart electrodes and the distal electrode, and wherein the microwave antenna includes a wire serially connecting each of the plurality of proximal spaced-apart electrodes. 